Torquing devices, such as wrenches, include coupling elements (torque adaptors) for coupling the device to a fastener, such as a nut or bolt, so that torque may be applied to the device for turning the fastener. The coupling element (coupler) may either be separable from the device, such as a socket that is separable from the remainder of a ratchet wrench, or it may be integral with the device, such as a closed or open ended box wrench. The term wrench is used herein to represent all types of coupling devices including the conventional socket, the closed end wrench, the open ended wrench and the box wrench.
The coupling elements have openings, such as cavities, formed therein which engage flat surfaces of polygonal shaped fasteners, such as nuts or bolts, to be turned thereby. Customarily, these wrench openings include a plurality of flat engagement surfaces, which are arranged in diametrically opposed parallel pairs. These surfaces are disposed, so as to parallel the shape of the fastener.
Standard dimensions and tolerances have been recognized for such wrench openings. These standards establish the permissible maximum and minimum clearances between the fastener and the wrench for each standard size, as well as the corresponding maximum and minimum angles of "free swing" of the wrench which can occur before contact is made between the flat surfaces of the wrench opening and those of the fastener. Obviously, the maximum permissible clearance and "free swing" will exist when a wrench, having the largest acceptable diametrical distance across the opening, is used with a fastener which has the smallest acceptable dimension diametrically across the flat surfaces thereof. Conversely, the minimum permissible clearance and "free swing" will exist when a wrench, having the smallest acceptable distance diametrically across the opening, is used on a fastener, which has the largest acceptable dimension diametrically across the flat surfaces thereof.
Due to this necessary range of permissible clearances, when an ordinary wrench is applied to a fastener and is rotated about its axis, the theoretical optimum contact between the flat surfaces of the fastener and the flat engagement surfaces of the wrench is not obtained. As a result, the contact between the wrench and the fastener occurs at or near at least a pair of diametrically opposite corners of the fastener (defined by the junction between adjoining, intersecting flat surfaces of the fastener). The net result is that theoretical line contact is not achieved, the torque transmission between the wrench and fastener is insufficient, slippage results, and the fastener is marred or damaged. Industry standards have been established to prevent initial contact between the socket and the fastener at the corner of the fastener.
Line contact frequently results in the build-up of such pressures that, especially at or near the maximum clearance, the corners of the fastener become mutilated, rounded-off and/or otherwise deformed. Accordingly, the torquing pressure that is, under normal conditions, already concentrated on a very small and easily distorted area of the fastener (the corners), is amplified along the line of contact, further, because of the wedging action between the engagement surfaces of the wrench opening and the corners of the fasteners, high spreading or bursting forces are built up in the head of the wrench which can crack, break and/or otherwise deform the wrench, especially when ordinary open end wrenches are involved. Such a condition creates a potential accident hazard, should the wrench suddenly slip around the corners under torque (due to deformation of the fastener and/or wrench).
In an attempt to overcome the above-mentioned problems, it has been proposed to provide wrench openings that engage the flat surfaces of the fastener in a surface-to-surface engagement while still providing the looseness and oscillary type play necessary, so that some "free swing" is still provided between the wrench and the fastener. To achieve this goal, it has also been proposed to equip the flat engagement surfaces of the wrench openings with angularly oriented planar engagement surface portions, whose angularity is selected in an attempt to provide the surface-to-surface engagement with the fastener when the mean tolerance spacing is present.
In U.S. Pat. No. 3,242,775 issued to Hinkle, a wrench is disclosed having an opening wherein each of the engagement surfaces of a wrench opening includes a central planar surface that is bordered on both ends by respective angulated surfaces. These angulated surfaces are also planar and are arranged and disposed relative to each other and to the planar surface at apices to form inwardly disposed apices at 61/2.degree. angles. The end of each angulated surface not forming the apices borders on one end of a respective groove having a curvature. The combination of the planar surface, an adjacent angulated surface and the apice formed therebetween, engages the tool to be removed.
In U.S. Pat. No. 3,495,485 issued to Knudsen et al, a socket is disclosed that has a geometric peripheral configuration of pairs of oppositely-inclined engaging surfaces for engaging and driving the tool, along with, and positioned between, concavities for providing complete tool corner disengagement. The angularity of the pairs of oppositely-inclined engaging surface are within a limited plus or minus range of 144.degree. outside and 216.degree. inside. The centers of the concavities alternating with the apexes formed at the junction of each pair of oppositely-inclined formed surfaces are symmetrically indexed on substantially 15.degree. angle emanating from the socket axis.
Other references which disclose wrench openings having angularly oriented planar engagement surface portions include U.S. Pat. Nos. 3,466,956 issued to Bowers, 3,903,764 issued to Andersen, 3,908,488 issued to Andersen and 4,512,220 issued to Barnhill, III, et al.
To further attempt to minimize the damage that can result from contacting the fastener near the corners thereof, it has also bee proposed to provide the opening of the wrench with convex or curved bearing surfaces that contact the flat surfaces of the fastener, so that surface-to-surface engagement, as opposed to line contact, between the fastener and the wrench is provided.
U.S. Pat. No. 4,581,957 issued to Dossier discloses a wrench opening having inwardly-convexed curved bearing surfaces disposed at either end of a straight surface. The curved bearing surfaces are the sole surfaces thereof that engage the flat surfaces of a tool desired to be removed thereby the curvature of these bearing surfaces is defined as being relative to the value of X by the formula: ##EQU1## One end of each of the bearing surfaces is adjacent to a respective groove while the other end of each bearing surface is adjacent to a respective planar surface. Neither these grooves nor the planar surfaces engage the tool to be turned.
U.S. Pat. No. 4,598,616 issued to Colvin, discloses wrench openings that have symmetrical inwardly-convexed curved bearing surfaces which engage the flat surfaces of the tool to be removed. The surfaces have curvatures including central portions. Each of the central portions of the engagement surfaces are spaced from a central axis by a radius R.sub.1. The curvatures of these surfaces have a radius of R.sub.2. R.sub.1 is defined as being from 0.06 R.sub.2 to 0.40 R.sub.2.
While aiding in alleviating the problems associated with line contact by providing surface-to-surface engagement in each of these references, contact still occurs between the engagement surfaces of the wrench opening and the flat surfaces of the fastener at or near the corners of said fastener. Some of the prior art is effective for a few sizes of sockets, but it is not consistent throughout the rang of sizes needed for all fasteners. Hinkle, for example, discloses a flank angle which does not vary with different sizes of wrenches or sockets. However, since 1965, no one has recognized that a constant flank angle produces damage to fasteners with certain sizes of wrenches or sockets and tolerance accumulations in manufacture of both sockets and fasteners. Despite this reference of long standing, such contact can still result in damage and/or deformation of the corners of the fastener, as described above.
Thus, it can be seen that there remains a need for a coupling element for a wrench and/or a wrench which incorporates a coupling element that has an opening therein for receiving a fastener to be turned thereby, which coupling element includes bearing surfaces that contact the flat edges of the fastener at a location that is spaced far enough from the corners defined therebetween, so that damage and/or deformation of the corner of the fastener is minimized.